Organise your library with keywords - Papers 3 for Mac

All keywords associated with a publication are displayed in the
overview tab of the inspector window.

If you don't have any keywords associated with a publication
click 'Add keywords' in the overview tab. You see a list of all the
keywords that you currently have in your library. If you want to
add an existing keyword to a publication, click on the keyword and
a tick mark appears next to the keyword indicating that the keyword
is now associated with the publication. If you have a long list of
keywords, use the filter bar to narrow down the keyword that you
want to include.

If you want to create a new keyword, type the keyword that you
want to add to the filter bar and hit the "+" sign to add it. Note
that the plus sign only appears once you type in something that
doesn't already exist as a keyword.

You can search your Papers library by keywords. To do so, click
on the arrow next to the library search bar and choose 'Keyword'
from the drop down menu.

You can view all publications associated with a certain keyword
in the Labels screen. Use the filter bar to narrow down a specific
keyword from a long list of keywords.

To edit or delete keywords, select a keyword that you want to
edit/delete from the list and click on the 'settings' icon (at the
very bottom of the left hand list) and select edit or delete
keyword.

You can also search for recent publications based on a selected
keyword. To do so, select a keyword and click on the 'settings'
icon to choose 'Show Recent Papers'. Alternatively, hover your
mouse next to the keyword to reveal a search loop.